1. Field of the Invention
Oil soluble olefin polymers are degraded to various molecular weights suitable for use as more shear stable Viscosity Index improvers for lubricating oil by heating in the presence of a free radical initiator in an inert atmosphere. By excluding oxygen during degradation the degraded polymer has a desirable, reduced tendency towards viscosity increasing interaction with other conventional lubricating oil additives such as ashless dispersants and detergent inhibitors. The degradation of the olefin polymer may take place before or during further reaction of the olefin polymer to form VI-dispersant additives. The invention includes the processes of producing the additives, the additives produced by the processes, and oil compositions containing the additives.
2. Prior Disclosures
Olefin or hydrocarbon polymers such as hydrogenated copolymers of isoprene and butadiene, copolymers of butadiene and styrene, and ethylene copolymers, particularly ethylene-propylene copolymers are known as viscosity index (V.I.) improving additives for oil compositions, particularly lubricating oil compositions. A substantial body of prior art exists directed towards further reacting these ethylene V.I. improvers to form a multi-functional V.I. improver. This is a material useful as a V.I.-dispersant oil additive so as to improve not only the V.I. properties of the oil but to also impart dispersancy so as to suspend sludge that may form during the operation or use of the lubricant and to inhibit varnish deposition in engines. For example, patents teach grafting ethylene copolymers with maleic anhydride, followed by reaction with an amine, such as U.S. Pat. Nos. 4,137,185, 4,144,181 and 4,089,794. Similarly, prior patents, such as U.S. Pat. Nos. 4,092,255, 4,146,489 and 4,170,561, were directed towards grafting the ethylene copolymer directly with a nitrogen compound such as vinyl pyridines and vinyl pyrrolidones. Various other patents, such as U.S. Pat. Nos. 4,068,056; 4,068,057 and 4,068,058, teach amines directly grafted upon an ethylene-propylene copolymer by mastication or by an extruder, either under a nitrogen atmosphere as U.S. Pat. No. 4,068,057 or in the presence of oxygen as in U.S. Pat. Nos. 4,068,058 and 4,068,056.
U.S. Pat. No. 3,862,265 has a broad disclosure of extruder-grafting a wide range of polymers including ethylene-propylene elastomers with various monomers, including maleic anhydride. U.K. Pat. No. 857,797 teaches grafting polymers by mastication using peroxide and in the presence of oxygen or air. U.K. Pat. No. 1,119,629 grafts maleic anhydride onto synthetic rubber in an extruder using inhibitors to control cross-linking. U.K. Pat. No. 832,193 has an extensive disclosure wherein various monomers were grafted by mastication upon various polymers using various techniques. The use of chain stopping agents or chain transfer agents have been suggested to inhibit cross-linking, as in U.S. Pat. No. 4,160,072; published Japanese Patent Application No. JA 53-110453 (Publication No. 55-36274) 1980, and in Japanese Patent Publication No. 46-35370 (1971).
It is also known to degrade olefin polymers to form a variety of lower molecular weight V.I. improving additive grades from a single starting grade that can be made in large volumes in a polymer plant. This also permits readily forming the lower molecular weight products which are difficult to directly make in a polymer plant because their low viscosity interferes with the usual polymer finishing steps. For example, U.S. Pat. Nos. 3,316,177 and 3,687,905 teach degradation as part of a grafting process while Canadian Pat. No. 991,792 teaches degradation by extrusion. European Published Patent Application No. 0123424 oxidatively degrades an olefin polymer in an inert solvent in the absence of molecular oxygen and in the presence of an oxidant mixture of at least one peroxide and at least one hydroperoxide.
One aspect of the present invention is based upon the finding that degrading the polymer in the presence of air can result in a polymer that will interact with other additives to give an undesirable viscosity increase, which degradation in the absence of air inhibits this interaction. It is not known with certainty why this interaction occurs, but it may be due to the formation of oxygenated sites such as ketones, aldehydes, acid carbonyls, etc. on the polymer, which later react or have an affinity with other additives to cause the viscosity growth. The present invention heats the polymer under nitrogen in the presence of a free radical initiator, which acts as a catalyst to speed up the degradation. Preferably, the degradation is carried out under shearing stress, which further speeds up the degradation. If the degraded polymer is to be used to form a V.I.-dispersant additive, the degradation may be carried out before, during, or overlapping the grafting or derivatization of the degraded hydrocarbon polymer to form a V.I.-dispersant additive. The present invention is a further improvement in forming useful oil soluble additives, wherein the degradation is carried out with the solid olefin rubber in the substantial absence of any chemical solvent. This avoids the need to remove the chemical solvent. Thus, the present invention can use a free radical generator when carrying out grafting in the solid state with an unsaturated monomer which may either be a nitrogen monomer or an unsaturated acid which can then be subsequently reacted, e.g. with an amine in a subsequent reaction to form oil soluble V.I.-dispersant additives.